This invention relates to synthesizer circuitry having a variable output frequency.
Synthesizer circuits are widely used in applications in telecommunications and other fields. A typical synthesizer contains a phase-locked loop that generates an output frequency that is an integral multiple of a reference frequency provided to the synthesizer by an resonator circuit. The output signal from such synthesizers may be used in wireless transmitter and receiver circuits.
Many synthesizer circuit arrangements are tunable. Typically, adjustments to the output frequency of the synthesizer must be made manually, by adjusting a mechanical variable capacitor in the resonator circuit that is used to provide the reference frequency to the synthesizer. However, such mechanically adjusted arrangements are susceptible to drift.
It is therefore an object of the present invention to provide a frequency-tunable synthesizer circuit that may be adjusted non-mechanically.
It is a further object of the present invention to provide a synthesizer circuit for a cordless telephone that may be adjusted so that its output frequency matches the frequency of another synthesizer.